343 research outputs found
On the Teleportation of Continuous Variable
The measurement procedures used in quantum teleportation are analyzed from
the viewpoint of the general theory of quantum-mechanical measurements. It is
shown that to find the teleported state one should only know the identity
resolution (positive operator-valued measure) generated by the corresponding
instrument (quantum operation describing the system state change caused by the
measurement) rather than the instrument itself. A quantum teleportation
protocol based on a measurement associated with a non-orthogonal identity
resolution is proposed for a system with non-degenerate continuous spectrum.Comment: 13 pages, no figures. To be published in JET
Measurement of the speed of sound by observation of the Mach cones in a complex plasma under microgravity conditions
We report the first observation of the Mach cones excited by a larger
microparticle (projectile) moving through a cloud of smaller microparticles
(dust) in a complex plasma with neon as a buffer gas under microgravity
conditions. A collective motion of the dust particles occurs as propagation of
the contact discontinuity. The corresponding speed of sound was measured by a
special method of the Mach cone visualization. The measurement results are
incompatible with the theory of ion acoustic waves. The estimate for the
pressure in a strongly coupled Coulomb system and a scaling law for the complex
plasma make it possible to derive an evaluation for the speed of sound, which
is in a reasonable agreement with the experiments in complex plasmas.Comment: 5 pages, 2 figures, 1 tabl
Resonant electron transfer between quantum dots
An interaction of electromagnetic field with a nanostructure composed of two
quantum dots is studied theoretically. An effect of a resonant electron
transfer between the localized low-lying states of quantum dots is predicted. A
necessary condition for such an effect is the existence of an excited bound
state whose energy lies close to the top of the barrier separating the quantum
dots. This effect may be used to realize the reversible quantum logic gate NOT
if the superposition of electron states in different quantum dots is viewed as
the superposition of bits 0 and 1.Comment: 8 pages, 1 EPS-figure, submitted to Phys. Rev.
Freezing and melting of 3D complex plasma structures under microgravity conditions driven by neutral gas pressure manipulation
Freezing and melting of large three-dimensional complex plasmas under
microgravity conditions is investigated. The neutral gas pressure is used as a
control parameter to trigger the phase changes: Complex plasma freezes (melts)
by decreasing (increasing) the pressure. Evolution of complex plasma structural
properties upon pressure variation is studied. Theoretical estimates allow us
to identify main factors responsible for the observed behavior.Comment: Phys. Rev. Lett. (in press); 4 pages, 4 figure
Renormalization Group in Non-Relativistic Quantum Statistics
Dynamic behaviour of a boson gas near the condensation transition in the
symmetric phase is analyzed with the use of an effective large-scale model derived from
time-dependent Green functions at finite temperature. A renormalization-group analysis
shows that the scaling exponents of critical dynamics of the effective multi-charge model
coincide with those of the standard model A. The departure of this result from the descrip tion of the superfluid transition by either model E or F of the standard phenomenological
stochastic models is corroborated by the analysis of a generalization of model F, which
takes into account the effect of compressible fluid velocity. It is also shown that, con trary to the single-charge model A, there are several correction exponents in the effective
model, which are calculated at the leading order of the = 4 − d expansion
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